Printing



Dec. 24, 1940. w. J. WILKINSON 2,226,086

PRINTING Original Filed Aug. 13, 1 935 .INYENTOR. Wdlzam J wdmizaan,

BY man/1% ATTORNEY.

Patented Dec. 24, 1940 PRINTING William J. Wilkinson, Eastchester, N.Y., assignor of one-half to Miehle Printing Press and MannfacturingCompany, Chicago, 111., a corporation of Illinois Original applicationAugust 13, 1935, Serial at. 36,019. Divided and this application August19, 937, Serial No. 159,896

- 5- Claims. (01. 101-4011) The present invention relates to the art ofgravure printing and concerns more particularly a novel intaglioprinting-plate, its process of manufacture, and an improved print fromthe plate presenting the original subject with great fidelity as to alltonal gradations.-

Intaglio printing, as at present ordinarly practiced, involves theemployment of a printing-plate made from a continuous-tone positive anda gravure-screen and in which plate the picture is depicted by a seriesof dots formed as ink-wells or depressions in the printing-surface ofthe plate,

and the printing from such plate when inked, the ink being carried inthe wells and pressure being applied to force the ink out of such wellsonto the paper or other surface, such method being commonly used, forexample, in the printing of Rotogravure sections of newspapers.

Such gravure printing, as usually carried out today, comprises theemployment of an intaglio printing-plate in which such ink-wells are allof the same area but which vary in depth in conformity with the tones ofthe original interpreted, the ink-wells representing the blacks orsolids of the subject being deepest, those corresponding to the lightesttones being shallowest, and those representing the intermediate tonesbeing of harmonizing intervening depths. Since the deeper wellsaccommodate a greater quantity of ink than the shallower ones, theformer of course, will deposit more ink on the paper and will,therefore,

produce darker tones. The image or design to be reproduced istransferred to the printing-plate by means of an intermediate medium,such as so-called carbontissue, through which the plate is etcheddifferentially to produce the ink-wells of varying depths, this beingthe only method employed commercially heretofore in making a gravureplate. Such printing-plate is ordinarily produced by first making acontinuous-tone negative of the subject and then making acontinuous-tone positive therefrom, the positive being photographicallyprinted on the light-sensitive gelatinous layer of the paper-backedcarbon-tissue, and a Rotogravure screen is also photographically printedthereover on the same light-responsive stratum of the carbon-tissue by asecond exposure. Such double-exposed carbon-tissue stratum or layer isthereupon secured face down on the surface of the metal printing-plate,its paper backing removed, and such coating developed, the developedcoating being known in the trade as a carbon-resist. The dots in suchcarbon-resist representing the different tones of the picture are all ofthe same size, which is determined by the equal areas of the screenopenings, but these dot areas, however, are unequally pervlous to theetching-fluid, depending on the tone of the zone of the subjectinterpreted. Etching-fluid then applied to such resist encounters lessopposition or resistance at those portions thereof corresponding to thedarkest zones of the original subject and greater resistance at thelighter zones, and it accordingly producesa deeper etch at the formerzones than at the latter zones where more resistance is encountered, theresist being more or less broken down or despoiled by the action of theetching-agent thereon during suchoperation. Owing to the varying degreesof permeability or hardness of the different sections of the resist dueto their previous unlike light-exposures, an etching-fluid or onespecific gravity only cannot be employed to etch the underlying platethrough theresist with the required result.

Accordingly, in practicing this procedure, five strengths ofetching-acid are ordinarily used progressively, the one of heaviestspecific-gravity being used first, and, after this has been removed, itsactionis followed up by those of successively less specific-gravities.Expert judgment and capable discretion on the part of the etcher arenecessary to determine the proper period of action of each strength ofthe etching-medium on the coated plate, After the etching has beencompleted, the carbon-resist is removed from the surface of the etchedplate.

The above-specified procedure involves various details and featureswhich are well-known to a person skilled in the art, the indicatedstepshaving been set forth merely by way of illustration and in order toaid in an understanding of the present invention and the benefitsaccruing from its employment.

Gravure-plates, formed as explained above, necessarily possess certaininherent disadvantages and limitations; positives are to be employed inthe production of a single, composite printing-plate, these positivesmust be of equal densities in order for all to be uniformly subject tothe action of the etchingagent, when they are simultaneously etched.Since the carbon-resist is destroyed during the etching action, theplate-etching 'operationcannot be stopped at will to permit examinationof the plate and the etching then continued, if required, to the correctpoint, due to the fact that when the carbon-resist becomes permeated orcharged with the etching-fluid, its continued disintegration cannot beprevented, and, accordingly, great skill is required on the part of theoperator to etch a plate having a given characteristic, and, the resultscannot be duplicated with any degreee of certainty. Furthermore, it ispractically impossible to obtain an accurate registration of the one ormore positives on the printing-plate because of the distortionintroduced by the employment 01' the carbon-tissue in transferring thesame to the plate.

A process of producing an intaglio printingfor example, it several such7 plate has heretofore been suggested comprisiig photographing thesubject in negative through a line-screen with the camera initiallyfocused to obtain a checkerboard effect of the screen on theground-glass of-the camera, over-exposing such negative-platesufficiently to cause the shaded and dark portions of the design of thesubject to appear on the negative as variable-size,entirelydisconnected, transparent dots, the largest dots correspondingin tone and position to the darkest zones of the subject, such excessiveor unusual light-exposure causing the negative, exceptfor the dots, tobe substantially opaque, and thereafter using this negative, through themedium of a positive plate or film made therefrom, an etch resist, andan etching-fluid to formthe intaglio printing-plate; or, stated somewhatdifferently,

substantially half of a complete screen tone range,

and then using a positive made from such negative to produce theintaglio-plate. The object of this extraordinary use of the ordinaryhalf-tone screen by over-exposure of the negative-plate through it is toobtain disconnected dots, instead of continuous solids, to represent thedarkest parts of the subject. In following this prior art method, thehalf-tone screen is spaced at its correct focal distance in front of thesensitive plate which is to constitute the negative and the excessivelight-exposure of the plate is depended upon entirely to lessen orrestrict the effect of the screen so that the negative carries only inhalf intensity the tones of the original subject. In accomplishing thisdesirable result, however, the over-exposure eliminates all dot effectsin the negative where the original subject was entirely white, so thatthe negative in those areas is completely opaque.

Whereas this procedure possesses merit an adapts itself for certainlines of work, such as textile printing, it has the disadvantage thatthe specified elimination of dot efi'ects is not restricted in thenegative to the completely-white portions of the subject, but such dotabsence applies also to the light tones of the original subject, wherebythis process does not result in the production of a print in exactconformity with all tones of the subject. Furthermore, such over- 7exposure exclusive of transparent dots in those parts of the negativecorresponding tothe whites of the original subject and to the adjacentlight tones thereof precludes the possibility of the introduction ofsuitable or proper dots in such light tones by reducing the negative.The over-exposure kills such dots beyond possibility of theirresurrection, and the result is that the print made from the positiveprinting-plate of such negative cannot faithfully and truly reproduceall tones of the original subject, those tones next to white necessarilybeing missing.

A leading purpose of the present new invention is to provide an improvedmethod of print: ing in which the several above-specified and otherdisadvantages apparent to a person skilled in the art are avoided oreliminated, an especial object of the invention being to supply adifferent and better procedure to overcome the deficiency of the secondof the prior art processes described, in that the new method is capableof making prints correctly and exactly representing all tones of thesubject from the lightest to the darkest.

Among the principal aims of the new invention may be mentioned (a) theprovision of an improved intaglio printing-plate and the process ofmaking the same (b) the production of a print having novelcharacteristics, (0) the improvement of the definiteness andregistration oi! the 5 final print, (d) a procedure of formingprintingplates which may be locally strengthened or lightened asrequired to correct tone values and (e) an improved process oftransferring a positive made through a half-tone screen to an intaglioprinting-plate, various other objects and advan tages of the inventionbeing made apparent as the natures of the details of the invention aremore fully disclosed hereinafter.

In the accompanying drawing, Figure 1 illustrates on an enlarged scaleand more or less diagrammatically, a face view of the novel hemitonegravure printing-plate constituting one part of the present invention;and

Figure 2 illustrates in similarmanner a gravure 20 or intaglio printproduced from such printingp a e.

In order that the novel intaglio printing-plate may have an ink-wellformation in its printingsurface capable of accurately representing alltones of the original subject, a positive-transparency is made byphotographing a continuoustone negative of the subject through aconventional half-tone screen under such conditions of screen-positionand of exposure that the dots on 80 the positive-transparency are all ofthe same intensity but vary in area or size from the darkest to thelightest tones, the blacks or solids of the original subject beingrepresented by practicallyunconnected dots and the whites of the subjectas being entirely free from dots in the positivetransparency, while thedots representing the intermediate tones are of correspondinglygraduated areas. Although such a positive-transparency is made throughan ordinary half-tone screen, nevertheless the positive-transparency isunique and diflers from an ordinary half-tone positive-transparency inthat the latter does not have the specified dot characteristics. Thisnew positivetransparency displays only about one-half of the 5 tonalintensities of the ordinary half-tone positive, that is to say, it hasonly about one-half the contrast or density of a conventional half-tonepositive, and for that reason it has been deemed well to characterize itas a hemi-tone" positive-transparency.

Stated otherwise, a special or unconventional, hemi-tonepositive-transparency is made from a continuous-tone negative of theoriginal matter for use in forming the intaglio-plate with which 55 theprinting is accomplished. In making this ex ceptional or peculiarpositive-transparency an ordinary half-tone or similar screen is soassociated with, or placed at such a distance in front of, thelight-sensitive plate or film on which the positivetransparency is to bemade and through which screen the light is projected onto the plate,that the darkest parts of the original subject, such as deep shadows,appear in this positive-transparency merely as intermediate,checkerboard or 68 middle tones, and the remainder of thepositivetransparency is comprised of all lesser tones graduatingproperly down to practically an absence of dots. This uncommon orunusual, hemitone positive-transparency, therefore, does not 70represent the originally-photographed subject correctly as to tonevalues, since it is much flatter in appearance because it incorporatesonly about one-half of the tone value or contrast of the original. Thispositive-transparency is unique in that, although it represents theentire range of tone values of the initial subject, all such values areactually present in the positive-transparency at about half intensity ofthe original, except pure whites which are the same in each. Thispeculiar positive-transparency is produced, not by overexposure, but byplacing the screen in front of the light-sensitive plate at the correctdistance, differing somewhat from its true focal distance, to producethe indicated result. The spacing of the screen in front of thephotographic-plate and the period of exposure of such plate are bothless than would be used to produce an ordinary, half-tonepositive-transparency with all other conditions the same.

Even the making of half-tone plates, as customarily practiced today, is,in a measure, a matter of trial due to the fact that the originalsubjects vary greatly, and heretofore there has been no satisfactory wayof preliminarily evaluating them which would render predeterminedprocedure always feasible or possible.

If in making the new specified hemi-tone positive-transparency, thecontrast therein is found to be too great to meet the conditionshereinbefore set forth, then the screen-distance should be somewhatdecreased, whereas, if such positivetransparency has too little contrastto comply with the specification, then a somewhat greaterscreen-distance should be tried.

Under usual conditions, the screen-distance may be about three-fourthsthat which would be used for the production of a half-tone and theexposure may be in the neighborhood of approximately onethird that whichcould be satisfactorily employed for the making of a half-tone; but itis to be understood that these factors are variable depending upon otherfeatures, such as the characteristics of the original subject, theintensity of the light, the speed of the emulsion, etc.

One skilled in the art, however, will experience no substantialdifliculty in producing a hemi-tone positive-transparency having theproperties referred to.

In this specification, where the term tone value or its equivalent hasbeen used in reference to the original subject, it is intended to meanthe relative position of the tone of any particular color in a scalewhich represents the full range of the color in question; when employedin relation to the continuous-tone negative, it signifies the value ofthe density or opaqueness of the tone; when used in reference to thehemi-tone positive-transparency, it specifies the relation between thetotal area of the opaque dots to the area of the trans parent surface ina unit area of the tone under consideration of thepositive-transparency, it being borne in mind that all dots in thepositivetransparency are of equal density regardless of size; and whenemployed in reference to the hemi-tone gravure printing-plate,hereinafter referred to in more detail, it means the relation betweenthe area of the ink-wells to the area of the non-printing surface in aunit area of the tone under consideration in the printing-plate.

To compensate for the stated absence of adequate and full-tone amplitudein this extraord-' permit a proper spreading thereof whereby to give theprint afull range of tone-gradation from the darkest shadows or solidsto the brightest highlights; this ink enlargement or spread of the dotson the print making good or overcoming the lack of full intensity of thepositive-transparency. Such spreading of the ink on the print takesplace in more or less degree for all printed dots.

One main reason for making and using such a singular or unexampledhemi-tone positive-transparency is this: If the positive transparencywere made with tones of theexact valuesin the original, the ink-wells inthe darkest portions of the etched metallic printing-plate would eitherbe run together into excessively large wells from which the ink-removingdoctor-blade would extract their ink or their walls would so thin thatthey would wear out unduly quickly with practically the same result.

Another, and perhaps preferable, mode of practicing the invention, whichprocedure is not however essential, but which has certain advantages ofaffording more leeway or greater latitude in the time of light exposurein making the positivetransparency and of the production of sharper andmore clearly defined dots and which may be accomplished by a slightchange in the indicated distance between the screen and the film whichis to form the positive-transparency, or by a slightly longer exposure,or both, comprises making a positive-transparency under conditions suchthat the whites of the subject have extremely fine dots in thepositive-transparency which are capable of being entirely removed by anordinary reducing operation, and, in eliminating these by suchreduction, all of the remaining dots of the positive-transparency willbe reduced a certain uniform extent, the specified reduction beingcontrolled so as to remove the dots on the whites without entirelyeradicating the dots representing the next darker shade.

In this way, all of the tone values of the picture are preserved,although the positive-transparency,

when viewed by itself, as stated above, shows less contrast and appearsflatter than the original subject. 7

A further principle of the invention resides in the transfer of thepositive-transparency directly to theprinting-plate without the use ofcarbontissue and in such a way that the subsequent etching can be easilycontrolled. To the accomplishment of this result, the surface of theprinting-plate is coated with a resist of such a nature that it remainssubstantially unimpaired and intact during the entire etching period,whereby the etching may be interrupted at any time, the plate examined,and certain areas painted out with a protective varnish or the like, asdesired, before continuing the etching.

The novel printing-plate possesses a non-printing surface correspondingto the whites of the picture and the remainder of which contains aplurality or aggregation of ink-wells representing the tone dots of thepicture, these Wells being of different areas and approximatelyuniformly etched as to depth, the wells representing the darkest tonesbeing practically separate and distinct, the tones next to white beingrepresented by small wells, and the areas representing the whites beingentirely free from wells. All of the ink-wells, however, aresufliciently deep to permit the plate to be topped, as by means of anresist has been removed, the applied ink acts as a resist whereby thewells may be etched deeper.

Various other capacities and characteristics of the invention willbecome apparent as the same is more fully disclosed in the followingdetailed description and pointed out with more particularity in theappended claims. i

More specifically, in producing the hemi-tone positive-transparency ofthe unconventional type, a. continuous-tone negative is made from theoriginal subject to be reproduced in the manner common in thephotographic art; but, if the original be a photograph, the negativefrom which it was made may be employed for this purpose, and, in eitherinstance, the negative may be retouched if desired.

For color work, a set of continuous-tone separation-negatives, one foreach color, is made photographically through color-filters in the usualway, and these are retouched or corrected as required so that eachnegative contains its proper color values.

Each negative, produced in this manner, is then placed before a camera,and while properly illuminated, is photographed through'an ordinaryhalf-tone or equivalent screen, the'exposure being such and the screenbeing so positioned with reference to the positive-transparency beingxnade that the dot-formation is produced on the positiveare so fine thatthey may be readily cut or removed in a reducing step. This desirabledotarrangement is obtained by selecting the proper distance between thehalf-tone or other screen (for example 150 lines to the inch) and thesensitized plate undergoing exposure and using the correct lens apertureand time for the exposure, such screen-distance and exposure both beingless than those which would produce an ordinary halftone positive withall other conditions the same.

This positive-transparency may be made on a wet-plate, if preferred, inorder that the subsequent development thereof may be more readilycontrolled; and, in the case of color work, when registration isparticularly essential, each of the positive-transparencies may hemadeby contact printing on a dry-plate using a.half-tone or similar screenin a manner such that the above-mentioned dot-formation is secured.

In either case, the positive-transparency is developed and then reducedby any standard reagent, depending upon the type of plate employed, and

during this procedure the entire positive-transparency is reduced asufiicient amount to eliminate entirely or substantially completely theminute dots on the whites, but not enough to eradicate the dotsrepresenting any of the next darker tones of the picture, this reductionstep also tending to remove any fringe effect of the dots and to causethem to be more clearly defined and with sharper demarcation. Thispositive-transparency, however, will appear to have less contrast thanthe original subject or the negative, this characteristic being ofmaterial importance in the subsequent step of printing with thecorresponding printing-plate, inasmuch as it provides a continuoussupport in the heavily inked parts of the plate for the ink-wipingdoctor-blade.

Expressed differently, this peculiar and noteworthy hemi-tonepositive-transparency is produced by using a half-tone or analogousscreen at assaose such a chosen distance from the light-sensitive filmas to provide the specified result with proper exposure, thepositive-transparency not truly depicting the negative from which it ismade, because it displays the tones of the continuous-tone, preferablybut not necessarily somewhat-thin, negative in discontinuous dots ofabout one-half less value or area than they should be, the result beingthat such positive-transparency looks unduly shallow or more or lesslifeless as it is without the full tone contrasts present in thecorrespond-v ing negative. If' such positive-transparency were made witha full gradation of tones and variations in density in complete andexact conformity with those of the negative from which it is made, thenthe portions of the plate etched therefrom presenting the deepestshadows, instead of having a large number of independentnicely-walled-in inkwells, would have relatively large areas of one welleach and of such size that there would be substantial danger of theink-scraping doctorblade scooping out their ink contents when it iswiping of! the excess ink-from the remainder o. the printing-plate. Bymaking this positivetransparency such that the deepest shadows or solidsof the original subject are represented by conventional middle tones,instead of full black tones, there is theassurance that the-ink-wellswillbe separate from one another with substantial intervening; 'walls;the; latter, as indicated, precluding theg'doctor-blade from extractingthe ink from the--larger wells.' It, is necessary, however,

to make amends for thislack-of full or adequate tone amplitudethroughout the positive-trans} parency,'and, accordingly, when theprinting-plate is etched through a resist made from suchpositivetransparency, the etching is carried to a sufficient depth inthe plate to permit each well to accommodate an amount of ink greaterthan that merely necessary to print a dot corresponding to the exactarea of the well, the result being that after each such dot is printed,its ink spreads on the print sufficiently so that the final print isdense enough throughout to present a true and correct reproduction ofthe original subject. i

From what precedes, it should be clear that in the hemi-tonepositive-transparency the solids of the subject are represented by dotsarranged in approximate checkerboard-design and it may be mentionedthat, when such dots are etched in the metal printing-plate, theactionof the etching-agent may round; out the sides of the correspondingk-wells somewhat but still retaining the general or approximatecheckerboard feature.

The; hemi-tone' positiv'ej transparency having been made in the.maiiiieiifindicated, it is ready for reproductionin theiprinting-plate.The surface of a copper-plate, which is to form its printing surface, issensitized by applyingthereto a light-sensitivecoatingofla solution ofshellac and a bichromate commonly called cold enamel." If the surface ofthe plate were covered with a thing coating of light-sensitive glue orgelatine, then exposed through a positive-transparency to the action oflight, and then developed, the coating would be so thin that it couldnot successfully resist the action of an etching-fluid, and to bring outits full acid-resisting properties, it must be baked. Such aglue-coating is known in the trade as a glue-top, and after the baking,it is characterized as a glue-enamel. Inasmuch as the specifiedcold-enamel coating is adequately resistant to etching-acid without thebaking required for the special glue-top, the tendency of a thin plate,when heated, to buckle or warp is avoided, and, in any case, it would bedifllcult to heat or bake a plate of large size properly and evenly.This unconventional and unprecedented hemi-tone positive-transparency isphotographically-reproduced in such light-responsive coldenamel coating,the positive having been previously stripped from its support and placedface down on the coating to assure that the final print will not bereversed right to left, whereupon such coating is developed, forexample, by the use of alcohol, leaving on the plate a coatingimpervious to the action of the etching-medium, but containing numerousfree small passages or openings therethrough corresponding to the dotsof the positivetransparency and through which the etchingfluid has freeand unimpeded access to the surface of the copper-plate. The positivedesign or picture is then etched through such resist apertures into thesurface of the underlying metal plate to the required' depth, a suitablesinglestrength only of the etching-agent being required. thus avoidingthe necessity for the great care heretofore essential if etchinggravure-plates.

In the use of this new method in color-printing, it has been found to beof the utmost importance to secure registration of all parts ofcooperating intaglio-plates, this being particularly essential in thecase of large subjects. Precise registration is facilitated by placingdependence on the employment for each color of the cold-enamellightsensitive coating on its copper printing-plate, which procedureentirely overcomes the normal and intrinsic uncertainties incident tothe use of a deformable or distortable carbon-tissue, such customaryintermediate tissue agency employed in the production of gravure-platesbeingsubject to serious inaccuracies which prevent the securing of fathful reproductions, because the gelatin and its paper support of thecarbon-tissue cannot be depended upon to afford correct registration dueto the vagaries of variable expansion with or across the grain of thepaper, the humidity and the temperature, of course, entering into thesituation.

Any areas of the printing-plate, such as borders, to be protected fromthe action of the etching-fluid, may be preliminarily painted over withasphalt-varnish, after which the unvarnished parts of the plate areetched with a standard etching solution for a sufllcient period of time,this op ration requiring from three. to eight minutes, depending uponthe solution employed. Such etching may be interrupted at any time topermit the plate to be washed, dried, and examined, because he res sthas remained in place in uninjured condition, and any portions of theplate hat have been adequately etched may be painted over w thasphalt-varnish before continuing the etching, which is then prolongeduntil the entire printing-plate has been etched the needed amount.

It is sometimes desirable to prolong the etching of t e darker portionsof the plate for a greater le--gth of time than the lighter sections inorder to produce ink-wells in those parts of the surface of the plate ofdepth enough to retain the re quired quantity of ink and all the wellsshould be etched to a depth such that the plate can be topped. ifdesired, for re-etching after the coldenamcl has been removed and aproof taken. The etching is terminated, however, before adjacent wellsbecome connected with one another in an material degree through thebreaking down of their walls. Such printing-plate may be cleaned andexamined at any time and re-etched as required prior to the removal ofthe cold-enamel, and, after the etching has progressed to the requiredpoint, the cold-enamel is removed by a strong cyanide or a lye solutionand the plate is then ready for the printing-press. After a proof hasbeen taken, the plate may be topped with ink and re-etched or correctedas needed, the ink, under these circumstances, acting as a resist.

In the finished, etched printing-plate, the various ink-wells are ofdifferent areas corresponding in position and size to the dots of thehemi-tone positive-transparency from which they were formed, but thesewells are of approximately the same depth. It will be understood,therefore, that use is made of conventional disconnected, middle-tonedots in the positive-transparency and corresponding conventional,practically-disconnected, middle-tone wells in the printing-plate forthe deepest shadows or solids and regular gradations from these todot-free or well-free whites, as the case may be, which are designed andadapted to faithfully and correctly reproduce all the tonal changes ofthe original in the print.

Again, this patentees disposition or system of hemi-tone ink-wells,since they are all of approximately the same depth, conforms to thegenerally-accepted, ordinary-half-tone formation, which is known torender a true tonegradation from solid to white and this does not applyto the commonplace, gravure, ink-well arrangement.

When this patentees inked plate in the printing operation, after itssurplus ink has been wiped off by the doctor-blade, is brought intocontact with the paper, which need not be of a superior grade, but maybe of the ordinary newspaper kind, the ink of all these numerous wellsis transferred to the paper and the ink of such multiplicity of printeddots spreads or expands on the surface of the paper in a manner toreproduce accurately and precisely all the tone-values of the initialsubject. It is the intention that the ink-wells in the plate insubstantial checker-board-design representing the blackest or deepestshadows or solids shall be of such size and capacity that, although theyare practically unconnected, the spreading of their ink (approximately100%) onthe paper will be suflicient to cover the entire area of theprinted surface corresponding to such portions of the subject, and theink employed should be of such viscosity, determined by the depth of theetching and of the separation of the Wells, that the dispersion of theink on the printed surface will thus faithfully duplicate all tones andshades of the original.

By the employment of the present invention with its non-requirement forthe use of carbontissue, the prints are produced with exact registrationfor color work, with the minimum amount of labor, with the leastcomplexity of operation, and with the fewest steps. These prints areoutstanding and noteworthy in that a selected restricted range of tonedots is made use of to represent all tone values of the originalsubject, none being omitted, and, although, in the shadows, theconventional middle-tone or checkerboard-arranged dots are present asvirtually, or to all intents and purposes, disconnected inkwells in theintaglio-plate, they are lost on the print through the adequatespreading of the ink to produce a rich ink layerforming a desirablecontinuous-tone.

Although the process set forth in detail above is one requiringreduction of the positive-transparency in the manner stated to removethe dots from the whites, it is to be remembered that this reduction isnot necessitated by reason of an over-exposure comparable to thatreferred to in one prior-art process and it is to be understood,furthermore, that the positive-transparencies can be made in a manner toavoid the original production of dots entirely in the whites of thepositive-transparency, and, accordingly, such a positive-transparencyrequires no reduction, although in such case the dots and {thecorresponding wells in' the printing-plate may not be quite as sharp asif the reduction method were followed.

Summarizing, somewhat, some of the paramount advantages and cardinalbenefits incident to the employment of the present invention, and whichare of marked commercial value, are as follows:-Once a properpositive-transparency has been made and knowing the gravity of theetching-fluid, the temperature, and the time period for the productionof a printingplate therefrom, any number of such plates. can be madewhich are, for all practical purposes, exactly alike, a resultheretofore incapable of accomplishment.' Again, persons of ordinaryability in the art may practice the new procedure with gratifyingresults and without resort to the highly technical skill and carefuljudgment which have been essential, in the past, in the making ofgravure-plates. Also step-and-repeat machines may be employed forcomposing the matter to be reproduced directly on the printingplates. Inaddition, local re-etching of the plate and continuation of the etchingmay be resorted to, if desired. Furthermore, faithful and exactreproduction of the original subject in the print is rendered possibleof accomplishment with ease and facility.

When the hemi-tone positive-transparency is made from the negative bythe direct-contact method and 150-1lne screen is employed, it has beenfound that the proper distance between the screen and the plateundergoing exposure is approximately .190 inch.

When such a positive-transparency is made in the camera, however, theoperator adjusts the screen to secure a correct position thereof toproduce a positive having the stated characteristics, but this does notmean that the hemitone positive-transparency will be like what theoperator sees on the ground-glass of the camera.

If the darkest tones of the subject are represented by quite small areasin the printing-plate, it is not essential that their ink-wells in allinstances be entirely disconnected, the principal aim being to provide aprinting-plate on which the ink-removing doctor-blade will have propersupport at all times so that it may efficiently perform its functionswithout withdrawing an undue quantity of ink from any of the wells.

The manners of practicing this invention have been described for thepurposes of illustration, but it will be apparent to persons skilled inthe art that various changes or modifications may be availedof and thatthe different features of the invention may be used in variouscombinations for the improvement of known printing processes. Theinvention is, accordingly, to be defined in accordance with the scope ofthe following claims when interpreted in view of the state of the priorart.

This application is a division of my co-pending patent applicationSerial No.'36,019, filed August of another of my co-pending applicationsSerial No. 755,649, filed December 1, 1934.

I claim:,

1. A hemi-tome intaglio printing-plate depicting at approximatelyone-half of their tonevalues all tones of an original subject, havingtones adjacent to white, by ink-wells of different areas etched in itsprinting-surface, the solids, if any, of the subject being representedby relatively-large, practically-unconnected ink-wells l0 occupyingapproximately one-half of each said solid area of the printing-plate andall lesser tones of the subject being represented by separated inkwellsof lesser areas in conformity with the tones which they depict.

2. A hemi-tone intaglio printing-plate depicting at approximatelyone-half of their tone-values all tones of an original subject, havingtones adjacent to white, by substantially-moirelessapproximately-equal-depth ink-wells of different areas etched in itsprinting-surface, the solids, if any, of the subject being representedby relativelylarge practically-unconnected ink-wells occupyingapproximately one-half of each said solid area of the printing-plate andall lesser tones of the subject being represented by separated ink-wellsof lesser areas in conformity with the tones which they depict.

3. A hemi-tone intaglio printing-plate depicting at approximatelyone-half of their tone-values all tones of an original subject, havingtones adjacent to white, by approximately-equal-depth ink-wells ofdifferent areas etched in its printingsurface, the solids, if any, ofthe subject being represented by relatively-largepractically-unconnected ink-wells in approximate checkerboard design,and all lesser tones of the subject being represented by separatedink-wells of lesser areas in conformity with the tones which theydepict.

4. An intaglio printing-plate depicting all tones of an originalsubject, having tones adjacent to white, by tone-values sufllcientlyless than those of an ordinary inverse half-tone, by ink-wells ofdifferent areas and of approximately the same depths, to represent thesolids, if any, of the subject by relatively-largepractically-unconnected ink-wells and to represent all lesser tones ofthe subject by ink-wells of lesser areas in conformity with the toneswhich they depict, a portion of said lesser tone ink-wells havingsubstantially circular contours, said printing-plate being characterizedin that any four of its ink-wells are grouped around a non-printing areaand have their centers located equi-distant from the center of saidnonprinting area, said non-printing area in all tones being neversubstantially less in size than that of any one of its said groupedink-wells.

5. An intaglio-print characterized by the fact that it represents areproduction of all tones of an original subject, having tones adjacentto white, by virtue of a substantially-even tone of velvety'naturerepresenting the solids, if any, the white areas of the print beingpractically free from dots, and the tones of the print between thesolids and the white areas being depicted by varying-sized dotscorresponding in areas to the tones v represented, said latter dotshaving more or less ragged perimeters, all ink portions of the print,solids and dots, being of substantially the same density, themiddle-tones of the print being formed of dots in substantiallycheckerbmrddesign and the tones of lesser values being represented byapproximately round dots.

WILLIAM J. WILKINSON.

